It is conventional practice to form photographic elements by forming on a support one or more photographically active layers. Typically these photographically active layers contain silver halide dispersed in a hydrophilic colloid, such as gelatin, to form an emulsion. In multi-layer photographic elements used in color photography there are at least three selectively sensitive color-forming units each made up of one or more emulsion layers coated on one side of a photographic support, such as film or paper. The color forming units are typically rendered variously responsive to the red, green and blue regions of the spectrum. The blue-sensitive color-forming unit typically contains a yellow coupler, the green-sensitive color forming unit a magenta coupler and the red-sensitive color forming unit a cyan coupler. In an alternative form color couplers are not initially present in the photographic element, but are introduced during processing after an image forming exposure. Hydrophilic colloid subbing layers, interlayers and protective layers are also typically present. The blue-sensitive color forming unit forms preferably the outermost unit, and a yellow filter layer normally overlies the green and the red sensitive color forming units to protect them against residual blue light not absorbed in the blue-sensitive color forming unit. Multi-layer photographic elements used in color photography of this general type and processes for their preparation are well known in the art.
Over the past several years, photographic manufacturers have focused on ways of conserving a valuable silver resource by lowering the coated weight of light-sensitive silver halide in photographic elements (S. Honjo, J. Imaging Tech., 15, 182 (1989)). However, it has been difficult to obtain a low silver-containing light sensitive material that does not compromise important image qualities like sharpness, speed, or graininess (European Patent Publication 0 629 909).
In Antoniades et al., U.S. Pat. No. 5,250,403, there are described photographic elements that use ultrathin tabular grain emulsions (less than 0.07 microns thick) in the top-most layer that provide distinct improvements in the specularity of the transmitted light and, thereby, an improvement in the acutance of underlying layers. In Sowinski et al., U.S. Pat. No. 5,219,715, there are described photographic elements having low coverage of certain tabular grain silver halide emulsions. However, the use of such ultrathin tabular grain emulsions is reported by one of the inventors in the above Sowinski patent to lead to significant speed losses (A. E. Bohan, G. L. House, J. Imaging Science and Tech., 38, 32 (1994)) because of the high front surface reflectance of these thin emulsions (Research Disclosure 25330, May, 1985). Thus, when these ultrathin tabular grain emulsions are employed in so-called "successive layer" structures that are conventionally employed in color photographic materials, such as for example when a support has provided successively thereon a red-sensitive layer, a green sensitive layer, and a blue sensitive layer, either a loss in speed or a diminution in another important photographic property would be expected to result.
It is also conventional practice to incorporate into photographic hydrophilic colloid layers addenda, referred to as hardeners, having as their purpose the reduction or elimination of the susceptibility of such colloid layers to wet abrasion, swelling in aqueous solutions and softening at elevated temperatures. Wet abrasion, swelling and softening are of primary concern during processing, especially in those instances where it is desired to accelerate processing by resort to elevated temperatures. Gelatin containing layers that are not treated with a hardening agent generally have poorer water resistance, heat resistance, and wet abrasion resistance.
After exposure to light, the photographic element is processed chemically to reveal a usable image. The chemical processing entails two fundamental steps. The first is the treatment of the exposed silver halide with a color developer wherein some or all of the silver halide is reduced to metallic silver while an organic dye is formed from the oxidized color developer. The second is the removal of the silver metal thus formed and of any residual silver halide by the desilvering steps of (1) bleaching, wherein the developed silver is oxidized to silver salts; and (2) fixing, wherein the silver salts are dissolved and removed from the photographic material. The bleaching and fixing steps may be performed sequentially or as a single step. The overall rate of development is influenced by swelling of the gelatin layer and diffusion rate of different chemical species into and out of the swollen emulsion layers. The diffusion coefficient value and emulsion layer swelling thickness increases with processing temperature and decreases with increasing hardness of the gelatin. When emulsion layer is hardened, the decrease in diffusivity is partially offset by the decrease in the swelling thickness and hence the decrease in diffusion pathlength. Therefore under given processing conditions, there is an optimum emulsion layer hardness for achieving desirable optical density or contrast or photographic speed.
The object of this invention is to provide a multilayer, multicolor photographic element where the imaging layers comprise a significant portion of silver halide tabular grains having a thickness less than 0.07 microns. The photographic element has well-balanced water swelling values in each dye-forming hydrophilic colloid containing silver halide emulsion layer and exhibits excellent photographic speed.